Male Amazon river dolphins pee into the air, confusing scientists

Yahoo

31-01-2025

Researchers say they have made a startling discovery in the Amazon River. But their evidence wasn't collected from the water—it could be seen from shore. After around 219 hours of observations, they can confirm that male Amazon river dolphins (Inia geoffrensis), also known as botos, often roll onto their backs and urinate over three feet into the air. It isn't random. The male botos appear to be peeing with a purpose.
Over four years, a team from Canada's CetAsia Research Group traveled to the Amazon river, where they then closely watched river dolphin social interactions. Researchers documented a total of 36 separate instances of male botos deciding to pee while floating in the unconventional position. The findings, presented in a recent study published in the journal Behavioural Processes, support rare, anecdotal stories of past boto behavior.
'Aerial urination starts with a boto slowly positioning itself upside down, exposing its penis above water, and ejecting a stream of urine into the air,' the team explained in their study.
What's more, another male dolphin was swimming nearby about two-thirds of the time, and often approached the urine stream as it landed in the water about three feet away. They sometimes waited in place, but in other instances, they even pursued the pee trajectory using their snout, or rostrum.'We were really shocked, as it was something we had never seen before,' study author Claryana Araújo-Wan recounted to New Scientist on January 31st.
Urine is a common communication tool used by many terrestrial animals such as dogs, bears, and cats. It's seen far less frequently in aquatic environments, but Araújo-Wan and their colleagues offered a few examples in their study. Dominant male African cichlid fish (Astatotilapia burtoni) interpret urine pulses for both reproductive and territorial information. The narrow-clawed crayfish (Astacus leptodactylus), meanwhile, urinates as a sign of aggression. In both of these cases, however, it's more about the act of peeing than what is actually in the pee itself.
This makes the boto behavior all the more interesting, according to researchers. Dolphins lack a strong sense of both smell and taste, so it's still somewhat unclear how they are interpreting the urine streams. The study's authors hypothesized that the male Amazon river dolphins may rely on their rostrum bristles to interpret their fellow boto's urine composition, such as hormonal content indicating physical health and social position. A previous study from a team at Stephen F. Austin State University in Texas confirmed bottlenose dolphins (Tursiops truncates) use their tongues to identify other cetaceans through the taste of their urine. Knowing this, it's also possible that botos in the Amazon may engage in similar activities.
But all that still doesn't explain why the botos are firing pee streams into the air. Researchers conceded that 'aerial urination likely serves a social function beyond waste elimination,' but stopped short of landing on any definitive reason beyond possible 'social or communicative functions.' Given their heightened ability to sense acoustical signals, it may be that the aerial urine alerts dolphins to check it out as it hits the water.
Regardless of the actual reason, confirming the unique behavior among Amazon river dolphins now opens up the possibility for future study. With more time—and more pee—researchers may eventually learn much more about the aquatic mammal's complex social dynamics.